An aide to a Republican congressman has resigned after her Facebook post criticising President Barack Obama's daughters touched off a backlash.

Elizabeth Lauten, communications director to Republican Stephen Fincher of Tennessee, said Malia Obama, 16, and Sasha, 13, should have shown more "class" at a turkey-pardoning ceremony last week at the White House, a presidential tradition for the harvest holiday of Thanksgiving, when Americans partake in a feast that features the turkey as its centrepiece.

She criticised the girls' casual dress and their behaviour - shrugs and eye-rolling greeted by most commentators with laughter at teenagers being teenagers.

Lauten wrote that the girls should "respect the part you play," and added: "Then again your mother and father don't respect their positions very much, or the nation for that matter, so I'm guessing you're coming up a little short in the 'good role model department.'"

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Lauten later apologised for the comments and deleted the original post, which drew harsh criticism across social media.

Jessica Carter, chief of staff for Fincher, said on Monday that Lauten resigned. Carter had no additional comment on a personnel matter.

After the post became the topic of conversation on a variety websites, Lauten issued an apology, saying "many hours of prayer," conversations with her family and a re-reading of her words made her reconsider the post.

"When I first posted on Facebook I reacted to an article and I quickly judged the two young ladies in a way that I would never have wanted to be judged myself as a teenager," Lauten told the Commercial Appeal of Memphis in an email. "Please know, those judgmental feelings truly have no place in my heart.

"Furthermore, I'd like to apologise to all of those who I have hurt and offended with my words."